Dear Amy: I’m a student living away from home. My parents have had some marriage difficulties. About two years ago, they told my sibling and me that they were thinking of separating.

At Christmas this year, my parents announced that my father would be moving out of the house. The next day, they took this back, and it was very confusing to us. Last summer my mother ran away from our home for the night. She lied about the trip, saying that it was for business, but we soon found out that it wasn’t.

Since then I have been very suspicious that she is cheating. I have logged on to her Facebook account to read her private messages. I discovered that she is having “sexy” conversations with a man in town and sending him nude photographs.

I feel very guilty about invading her privacy, but I feel more upset at my mother for doing this while still married to my father. I consider this cheating.

I’m afraid to bring up this topic with my mother because it involves my disclosing information that I invade her privacy on a frequent basis (to check these Facebook messages). And I don’t want to tell my father to save him from this pain. I feel quite guilty for not telling him and also afraid of my mother’s wrath if I tell her.

What should I do? Which one do I bring this up with first? Or should I stay out of it? — Distressed Daughter

Dear Daughter: Marriage is complicated. So, sometimes, is cheating. But don’t double-down on your mother’s cheating by being dishonest and sneaky.

I understand your motives, but you are jumping to conclusions based on evidence with absolutely no context.

If you had access to the whole truth you might find: Your father already knows about this, and they are trying to work things out. Or perhaps your father’s own Facebook messages are also inappropriate and adulterous.

Even if your conclusions are 100 percent correct, are you prepared and able to leap into the middle of your parents’ relationship to confront and/or comfort them? This is waaaaaay above your “pay grade.”

I suggest you tell your mother that you are aware of her activity on Facebook. Assume that she will be appalled at your sneakiness. Tell her you are confused by what they have put you through.

This is a big mess, but your parents — not you —are going to have to figure things out.

Dear Amy: My daughter’s in-laws have made it known that they only want Easter pictures of her new baby by herself and not with her brother (who is from a previous marriage).

The baby is 6 months old, and the brother is 7 years old.

My daughter is very upset. How should she handle this? — Sad Gran

Dear Gran: The implication here is that these grandparents don’t want to see your daughter’s children as “real” siblings or as equal grandchildren and that there is only room enough on their refrigerator (or in their hearts) for their bio-granddaughter.

Your daughter should start by asking her in-laws why they only want a photo of the baby alone. Perhaps they have a logical reason.

These grandparents may not understand what a tender issue this can be for a family that is working hard to blend and be “real.” Or perhaps they do understand, and they’re being thoughtless and hurtful.

Your daughter (and especially her husband) will have to help them understand that this family is a unit and that the brother and sister are like other brothers and sisters — photographed together during happy holidays.

The parents should not tolerate exclusion but should also give these grandparents time to catch on.

Dear Amy: The recent letter from “Upset” really upset me. She detailed a relationship in which she was now “hooking up” with a former boyfriend who simply treated her like a booty call.

And yet, she was pining to be with him.

I was in a relationship like this, and it took literally years from my life. I hope Upset gets a clue. — Survivor

Dear Survivor: She wrote to me for a reason. I hope clue-getting followed publication.

My husband and I are retired. We married 12 years ago — several years after his ex had an affair and left him. My husband has two grown sons (around 40), one of whom is married. The married son and his wife essentially ignore that I exist.